The PLCO Central Data Coordinating Center (CDCC) is an extension of the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial. To reduce costs, the extension has one data collection site under the direction of the National Cancer Institute (NCI) rather than the original ten PLCO Screening Centers. PLCO participants were invited to be transferred to the CDCC for continued, active follow up. Other participants agreed to be passively followed at the PLCO sites through tumor registry searches. PLCO was designed to determine if screening for prostate, lung, colorectal and ovarian cancer can reduce mortality from these cancers. In addition, PLCO has a collection of pre- and post-diagnostic biological samples stored in the PLCO Biorepostory, and epidemiological data from questionnaires. These data are a valuable resource for cutting-edge molecular epidemiologic research. The study was extended in this streamlined fashion to increase the value of the resource. The study will continue to update key exposure data by collecting additional risk and lifestyle information, including medication use and medical conditions that are common in older adults. Also, the CDCC will collect additional clinical data and tumor tissue of selected cancers, such as that of the colon and ovaries. This extension of the PLCO Cancer Screening Trial enhances the value of the PLCO resources through the substantial increase in the number of incident cancers accrued within the Trial, strengthens the Trial's ability to clarify further the long-term effects of screening on cancer mortality, and provides a final opportunity to collect additional exposure data and expand the existing tumor pathological resource within the PLCO.